Japanese Patent Application Laid-Open Publication No. 09-148325 (Patent Document 1) discloses techniques capable of obtaining a silicon oxynitride film excellent in in-plane film thickness uniformity and electrical characteristics. Specifically, a semiconductor substrate is subjected to a thermal treatment, thereby forming a silicon oxide film on the semiconductor substrate (oxidation step); and then, the silicon oxide film is nitrided by a thermal treatment using ammonia (NH3), thereby forming a silicon oxynitride film (nitridation). Subsequently, a thermal treatment using nitrogen monoxide is carried out, thereby removing hydrogen contained in the silicon oxynitride film (dehydrogenation).
In Japanese Patent Application Laid-Open Publication No. 2000-77546 (Patent Document 2), a silicon oxide film is formed on a semiconductor substrate. Then, a thermal treatment is carried out in an atmosphere of nitrogen monoxide, thereby forming a first silicon oxynitride region A and a second silicon oxynitride region B which contains a relatively smaller amount of nitrogen than the first silicon oxynitride region A.
In Japanese Patent Application Laid-Open Publication No. 06-209009 (Patent Document 3), a method of forming a silicon oxynitride film which is expected to be used as an alternative for a silicon oxide film is described. Specifically, a technique of forming the silicon oxynitride film by nitriding the surface of a silicon substrate, then forming a silicon oxide film thereon, and densifying the silicon oxide film is described.
In Japanese Patent Application laid-Open Publication No. 06-291330 (Patent Document 4), a technique below is described. Specifically, a semiconductor substrate is subjected to a thermal treatment at a temperature of 950° C. and in a nitrogen-diluted oxygen atmosphere, thereby forming a silicon oxide film on the semiconductor substrate. Then, the silicon oxide film is nitrided in an ammonia atmosphere at 1000° C., thereby forming a silicon oxynitride film between the silicon oxide film and the semiconductor substrate.    Patent Document 1: Japanese Patent Application Laid-Open Publication No. H09-148325    Patent Document 2: Japanese Patent Application Laid-Open Publication No. 2000-77546    Patent Document 3: Japanese Patent Application Laid-Open Publication No. H06-209009    Patent Document 4: Japanese Patent Application Laid-Open Publication No. H06-291330